Handoff metric for multiple transmission technologies

ABSTRACT

Provided are methods and systems of managing a handoff in a multimedia communication network. Embodiments include estimating the voice quality of a communication route in the network. The voice quality may be estimated by using a total voice quality metric involving subtracting various impairments to the voice signal. Impairments may result from the type of vocoder in a communication route, the error or loss associated with RF links and network links, and delays in the communication route. After subtracting the impairments to obtain the total voice quality metric for the communication route, the total voice quality metric may be compared with a threshold and/or other total voice quality metrics of other communication routes to determine whether and when a handoff should be made.

BACKGROUND

The subject matter disclosed herein relates to communication systems,and more particularly, to systems and methods of conducting handoffsbased on voice quality of a communication.

A communication system may include communication devices capable oftransmitting and receiving human speech. For example, a user may speakinto a first communication device, and the speech waveform may becompressed and digitized and then transmitted to a second communicationdevice. The compressed digital signal may be decompressed to reconstructan approximation of the original speech waveform. The compression anddecompression of speech signals in a communication system may involvevoice encoders, commonly referred to as “vocoders.”

Communication devices may be connected within a network throughdifferent communication routes. Each communication route connecting adevice within the network may include a link between the device and avocoder. The vocoder may be linked to a network node, which may beconnected through its own subnetwork within the communication network. Acommunication network may have multiple communication routes, as thenetwork may include multiple subnetworks, network nodes, and vocoders.The particular communication route of a communication device may dependon the signal strength between the device and the node. As signalstrength may change during a communication, the link between a deviceand a node may sometimes be switched to maintain an acceptable signalstrength. For example, a connection between a communication device and afirst network node may be switched to enable a communication between thedevice and a second network node for increased signal strength. Such aswitch in communication between device and network node may be referredto as a “handoff.”

As communication systems evolve, other parameters in addition to signalstrength may be used in conducting handoffs in a communication network.While signal strength may be used as a metric for conducting a handoffbetween network nodes connected to a fixed circuit-switched landline,signal strength alone may be an inadequate metric for conductinghandoffs in a multimedia communication network using a multi-hoppacket-switched system. A multimedia network system may includedifferent types of wireless services (e.g., cellular services and VoIPservices) which transmit packets over different links (e.g., fixed linksor radio frequency links) having different frequencies and differentdegradation characteristics. Furthermore, different communicationtechnologies may use vocoders having different architectures orincompatible bit streams, which may also affect speech transmission.Thus, using a metric more suitable for a multimedia communicationnetwork may improve communication quality.

BRIEF DESCRIPTION

One embodiment includes a method of managing a communication in acommunication network. The method includes estimating a total voicequality metric for a communication route in the communication networkand controlling a handoff based on the total voice quality metricestimation.

Another embodiment includes a method of managing a handoff in amultimedia communication network. The method includes computing avocoder impairment based on the vocoder selected for a communicationroute in the network, computing a radio frequency (RF) link impairmentbased on one or more RF links selected for the communication route,computing a subnetwork impairment based on the subnetwork selected forthe communication route, and computing a delay impairment based on atotal delay incurred in transferring data through the selected vocoder,the selected one or more RF links, and the selected subnetwork. Themethod includes computing a total voice quality metric of thecommunication route based on the vocoder impairment, the RF linkimpairment, the subnetwork impairment, and the delay impairment anddetermining whether and when to make a handoff based on the total voicequality metric of the communication route.

Yet another embodiment includes a communication system which includesmemory configured to store vocoder information corresponding to one ormore vocoders in the system, a processor configured to calculate thevoice quality of a communication route based at least on the vocoderinformation and configured to conduct a handoff based at least on thevoice quality of the communication route.

Yet another embodiment includes a method for managing a handoff in acommunication network. The method includes estimating a voice qualityfor a communication route in the communication network. Estimating thevoice quality includes determining one or more impairments to the voicequality of the communication route, subtracting the one or moreimpairments from the voice quality to produce the voice qualityestimation, and controlling a handoff based on the voice qualityestimation.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a diagram depicting possible routes in a portion of amultimedia communication network, in accordance with embodiments of thepresent techniques;

FIG. 2 is a table including possible impairment contributions to speechtransmission in a communication network, in accordance with embodimentsof the present techniques;

FIG. 3 is a diagram depicting how data corresponding to possibleimpairment contributions to speech transmission may be stored and/orcomputed in a communication network, in accordance with embodiments ofthe present techniques; and

FIG. 4 is a flow chart summarizing a process for managing a handoff in amultimedia network, in accordance with embodiments of the presenttechniques.

DETAILED DESCRIPTION

A communication system may include the wireless transmitting andreceiving of human speech from one communication device to another. Forexample, a communication (i.e., a transfer of human speech from onedevice to another) may be in part enabled by the connection ofcommunication devices within a communication network. In a communicationnetwork, a device may communicate with other devices in the network byconnecting to the network via links with one or more network nodes. Thenetwork node may be linked to controllers or gateways, which may belinked to a common communications medium (e.g., a wired telephonenetwork), such that all devices in the network are connected.

A communication between two devices in a network may include acommunication route of links connecting two devices. A “link” may referto a connection, a transferred signal, etc., between a communicationdevice, a vocoder, network node, and/or a controller in the network. Acommunication route may refer to a series of links which connect adevice to a communication medium in the network. A processor in thecommunication network may conduct the linking of devices in the network,and may link the communication device to a selected vocoder or aselected network node based on which links may have the highest signalquality. For example, in an embodiment, signal quality may includemetrics such as signal strength and voice quality. During the durationof the communication, the signal quality between a communication deviceand a network node may change. To maintain a communication havingacceptable signal qualities, the processor may link the communicationdevice to a different network node. It may be desirable for such atransfer, referred to as a switch in communication or a “handoff,” tooccur with relatively little delay, such that the handoff may besubstantially unnoticeable to a user of the communication device duringthe communication.

For example, a diagram depicting possible communication routes in aportion of a multimedia communication network 10 is illustrated inFIG. 1. A communication device user 12 may be connected to acommunication medium such as the wired telephone network 30 via manydifferent non-overlapping routes of links. Each route may include achoice of one or more vocoders 14 a, 14 b, 22 a, 22 b, and 22 c whichare connected through wireless communication links 16 and 24 to anetwork node 18 and 26. The network nodes 18 and 26 may then beconnected to the wired telephone network 30 through their ownsubnetworks 20 and 28. The subnetworks 20 and 28 may each include othernetwork nodes or controllers of network nodes. While the illustratedportion of a multimedia communication network 10 is used as an exampleof one type of communication network for which the present techniquesmay be implemented, methods of managing handoffs in a multimedia networkmay also be implemented between different types of wireless networks andmay include various other devices (e.g., different types ofcommunication devices, network nodes, and controllers) which may not allbe illustrated in the network 10.

The multimedia network 10 may also include a processor 32 which maysubstantially control links between one or more devices in the network10. For example, the processor 32 may be coupled to the wired telephonenetwork 30, and in some embodiments, the processor 32 may be coupleddirectly to network nodes or communication devices. The processor 32 maydetermine various parameters corresponding to the links in a network 10,and may also conduct handoffs based on an analysis of the linkparameters. In some embodiments, the processor 32 may calculateparameters such as estimated voice signal impairments or total voicequality metrics for various communication routes.

A typical method of conducting a handoff within a network may includeusing a signal strength handoff metric. Using a signal strength handoffmetric may be efficient for networks having cellular base stationsconnected to fixed circuit-switched landlines. However, communicationsystems have evolved, and a typical multimedia network system mayinclude different types of wireless services in addition to cellularservices, such as, for example VoIP services. For example, the networknode 18 may represent a cellular base station used to connectcommunication devices in a cellular service, and the network node 26 mayrepresent a VoIP access point used to connect communication devices in aVoIP service. Each of the different types of wireless services in amultimedia network 10 may use different types of links, such as link 16which connects a vocoder 14 a or 14 b to the base station 18, or link 24which connects a vocoder 22 a, 22 b, or 22 c to the access point 26.These different types of links 16 and 24 may transfer data overdifferent routes, medium, and/or frequencies. For example, a cellularnetwork may use radio frequency (RF) links, while a VoIP network may usea multi-hop packet-switched connection, and may have only one RF-basedlink (e.g., the wireless link between a network node 26 and a selectedvocoder 22 a, 22 b, or 22 c). Due to the different types ofcommunication links 16 and 24 used in a multimedia communication network10, the transferred data within the network 10 may also experiencedifferent degradation characteristics. Furthermore, different wirelessservices may also use vocoders in the encoding and decoding of voicesignals. For example, vocoders 14 a and 14 b may have differentarchitectures or incompatible bit streams with vocoders 22 a, 22 b, and22 c. Such differences in vocoder types used for different wirelessnetworks may also affect speech transmission and complicate typicalhandoff techniques.

As data transfers differ across the different types of wireless servicesin a communication network, signal strength may be an insufficientdeterminant of the quality of a communication. For example, bit errorrate (BER) may be a typical metric used to measure signal degradation.However, while a single bit error may result in a packet drop in a VoIPlink (e.g., link 24), such a bit error may be unnoticeable by a usercommunicating through a cellular link (e.g., link 16). Thus, if amultimedia network conducts handoffs solely based on signal strength(e.g., handing off at some threshold level of signal degradation orBER), handoffs may be conducted during a communication even if thecommunicating users would have experienced no perceptible loss in voicequality. Conducting such unnecessary handoffs in a multimedia networkmay lead to complexity and/or inefficiencies in the network. Forexample, ping-ponging could result when signal quality oscillations leadto rapid handoffs, which may lead to delays in a communication.

In some embodiments, a multimedia network 10 (or a processor 32 in thenetwork) may conduct handoffs based on a quality metric which may besuitable for evaluating communication quality over different types ofwireless links. For example, in some embodiments, a “total voice qualitymetric” may be used to conduct handoffs in a multimedia communicationnetwork. The total voice quality metric may include certain aspects ofsignal strength, but may not be merely a measure of signal strength.Determining the total voice quality metric may include otherconsiderations which affect the voice quality of a voice signal that isspoken by one user and heard by another user during a communication.Additional considerations may include different impairments (e.g.,degradations which affect the quality of the final transmitted voicesignal) over various communication routes in a multimedia network 10which may affect the quality of the voice signal during a communication.Such impairments may be determined and/or quantified using variousmetrics to determine the total voice quality metric. For example, avoice quality metric may include the International TelecommunicationUnion (ITU) E-model defined in Recommendation G.107, which provides aprediction of the expected voice quality as perceived by a communicationdevice user. The E-model may account for any predictable sources ofvoice quality impairments along a communication route (from a speaker ofone communication device to a listener of a second communication device)under typical communication conditions.

The voice quality prediction of the E-model may be an additive linearvoice quality rating referred to as the R-factor or the R-score, and maybe on a scale from 0 to 100. For example, in one embodiment, a score of100 may be considered high voice quality, a score of 75 may beconsidered medium voice quality, and a score of 50 may be considered lowvoice quality and may result in a handoff. In other embodiments, anyclassifications or thresholds based on the R-factor may vary, and anyhandoffs conducted based on the classifications or thresholds of theR-factor may also vary.

A table 50 including possible impairment contributions used to determinea total voice quality metric for a speech transmission in acommunication network is provided in FIG. 2. To further illustrate thequality metric concept, the table 50 may be adapted to the multimediacommunication network 10 of FIG. 1, and may provide a total qualityscore 60 for each of the five possible communication routes in FIG. 1,where a different vocoder (14 a, 14 b, 22 a, 22 b, or 22 c) is selectedin each route. The total voice quality metric may be represented by thetotal quality score 60, which may refer to a quality of a voice orspeech signal as perceived by a communication device user.

In one embodiment, the impairment contributions in each communicationroute may include vocoder impairments 52, RF link impairments 54, andsubnetwork impairments 56. Such impairments may be determined, forexample, using methodology similar to that found in ITU-T RecommendationP.833. Vocoder impairments 52 may include baseline quality impairments,impairments due to bit errors or packet losses (BER or PLR), andalgorithmic delays of the vocoders. The baseline quality impairments mayrepresent the quality of the vocoder itself with no bit errors or packetlosses, and may be subtracted from the R-score. The impairment factordue to bit error or packet loss may result from low signal levels on anRF link or packet loss on a congested subnetwork link. The bit errorimpairment factor may be multiplied by the BER in a bit-oriented link toproduce a number that is subtracted from the R-score. The BER impairmentmay also be used for a conventional circuit connection similar to acellular RF link. The packet loss impairment factor may be multiplied bythe PLR in a packet-switched network to produce a number that issubtracted from the R-score. Unlike the BER impairment, the PLRimpairment may not be relevant for a circuit-switched link. Thealgorithmic delays may be the total delay from the vocoder based on theframe sizes used in compressing and decompressing voice signals. As willlater be discussed, the delays from the vocoder may be combined withother delays along a communication route to determine an impairment fromtotal delays. The vocoder impairments 52 may be known in advance, sincethe vocoders used in a communication network 10 may have knowncharacteristics.

A communication route may include any number of links which transfer thedata to enable communication between two devices, and impairments tovoice quality may result from any of these links. For example, acommunication route involving vocoders 14 a or 14 b may also includelink 16 which contributes to RF link impairments 54 and any links in thesubnetwork 20 which contribute to subnetwork link(s) impairments 56.Similarly, a communication route involving vocoders 22 a, 22 b, or 22 cmay also include link 24 (contributing to RF link impairments 54) andany links in the subnetwork 28 (contributing to subnetwork link(s)impairments). Each link in a communication network 10 (FIG. 1) may beclassified as either packet-switched, meaning the link may be degradedby packet losses, or bit-oriented, meaning the link may be degraded bybit errors. For packet-switched links, the PLR may be measured andmultiplied by the vocoder loss impairment factor of the correspondingvocoder used in that particular communication route (e.g., vocoder 14 aor 14 b for link 16). For bit-oriented links, the BER may be measuredand multiplied by the appropriate vocoder error rate impairment factors.The resulting numbers may be subtracted from the R-score.

The total delay may be calculated by summing all delays in acommunication route, including the vocoder algorithmic delay and allindividual link delays. The impairment from total delay 58 may then becalculated using equations 3-27 and 3-28 from Recommendation G.107 ofthe ITU E-model. The equations (renumbered) are reproduced below:

$\begin{matrix}{{{Idd} = {25\left\{ {\left( {1 + X^{6}} \right)^{\frac{1}{6}} - {3\left( {1 + \left\lbrack \frac{X}{3} \right\rbrack^{6}} \right)^{\frac{1}{6}}} + 2} \right\}}}{and}} & \left( {{equation}\mspace{14mu} 1} \right) \\{{X = \frac{\log\left( \frac{Ta}{100} \right)}{\log\; 2}},} & \left( {{equation}\mspace{14mu} 2} \right)\end{matrix}$where Ta may represent the summed total delay and Idd may representimpairment from total delay.

The impairment from total delay 58 for each communication route may alsobe subtracted from the R-score. Therefore, subtracting all impairmentsin each communication route, results in the total quality score 60 foreach communication route. The calculation for the total quality score 60may be represented in the equation below:Rs=R ₀ −Iv−Irf−Isn−Idd  (equation 3),where Rs represents the total quality score 60 for each communicationroute in a network. R₀ represents a perfect R-score with no impairments,Iv represents the impairment from the vocoder used in each communicationroute (including basic vocoder quality but excluding BER or PLRimpairments of the vocoder), Irf represents the impairment from the RFlinks arising from BER/PLR losses (which are computed by multiplying theRF error or loss rate by the vocoder error or loss impairment factors,respectively), Isn represents the impairment from other links in thesubnetwork arising from BER/PLR losses on the subnetwork (which arecomputed by multiplying the subnetwork error or loss rate by the vocodererror or loss impairment factors, respectively), and Idd represents theimpairment from total delay (including the delays arising from thevocoder itself and delays summed from each portion of a communicationroute, and calculated using equations 1 and 2 above).

A summary of the table 50 explained in FIG. 2 is provided in FIG. 3,which illustrates a diagram of where and/or how the communication routedata of the table 50 may be stored and/or computed in a communicationnetwork 10 (as in FIG. 1). Certain data relevant to determining thetotal quality score 60 may be known in advance and may be stored in anetwork information query unit 62. The network information query unit 62may include memory suitable to storing network information, and may beaccessible by a processor (e.g., processor 32 in FIG. 1) which may usecommunication rate data to manage handoffs in a network. In oneembodiment, the vocoders used for different communication routes in anetwork may be pre-determined, and impairments associated with vocoders(Iv 52 and the BER/PLR loss impairment factors) may be known in advanceand stored in the network information query unit 62. Some impairmentsassociated with subnetworks (Isn 56) may also be stored in the networkinformation query unit 62. Furthermore, delays from vocoders (e.g.,algorithmic delays inherent to vocoders) and subnetwork delays maycontribute to the total delay (Idd 58), and such delay information mayalso be stored in the network information query unit 62.

As each subnetwork (e.g., subnetworks 20 and 28 in FIG. 1) may includemultiple possible links (e.g., between network nodes or controllers), amulti-link ping unit 66 may be used to compute the delays associatedwith data transfers for communication routes within the subnetwork(e.g., sub-routes). The multi-link ping unit 66 may also calculate datalosses incurred in each sub-route of a subnetwork. The computed lossesand delays associated with different sub-routes in a subnetwork may alsobe used to determine a total quality score 60 to be used in managinghandoffs in a multimedia network 10.

Each communication route may also include an RF link. Depending on thetype of wireless services used in a multimedia network 10, acommunication route may predominantly use RF links (e.g., cellularsystems), or may involve a multi-hop connection and use a RF link as alast step in a communication route (e.g., VoIP systems). Thus, theimpairments contributed by RF links for different communication routesmay vary significantly in a multimedia network 10. Furthermore, ascommunication device users (e.g., user 12) may constantly move relativeto a network node with which the device is linked, the RF links maychange throughout a communication, thus changing the impairmentscontributed by the RF links in the communication route of the user 12.RF link impairments (Irf 54), as well as delays associated with RFlinks, may be computed by the RF link quality analysis unit 64, and insome embodiments, the RF link quality analysis unit 64 may compute RFlink impairments 54 dynamically. The RF link quality analysis unit 64may be part of a processor 32 in the network 10, or may be a separateprocessing unit capable of analyzing RF link impairments 54 and usingthe impairment data to manage handoffs in a multimedia network 10.

Information stored in the network information query unit 62 and theinformation computed by the RF link quality analysis unit 64 and themulti-link ping unit 66 may all be used to manage handoffs in amultimedia network 10. For example, a processor 32 may use theinformation stored in and/or computed by the different units 62, 64, and66 to manage a crossbar switch 68 which enables a handoff by switchinglinks in communication routes. The crossbar switch 68 may be any switchcapable of switching links (and thus changing communication routes) in amultimedia communication network 10.

FIG. 4 provides a flowchart summarizing a process 70 for managinghandoffs in a multimedia network 10 in some embodiments of the presenttechniques. The process 70 may include estimating (block 72)impairments, including impairments along a communication route. Aspreviously discussed, the impairments may be contributed by the vocoders(Iv), the subnetworks (Isn), or the RF links (Irf) in a communicationroute. The transfer of data through vocoders, subnetworks, and RF linksmay also result in delay, and these delays may be summed (block 74). Thesum of the delays may be used to compute (block 76) a delay impairment(Idd), using, for example, the previously provided equations 1 and 2.All impairments may be subtracted (block 78) from an R-score to producethe total quality score 60 of a communication route. The total qualityscore 60 of a communication route may be used to conduct handoffs (block80). For example, a processor 32 may compare the total quality score 60of several communication routes to determine when and/or whether ahandoff is to be conducted for a particular communication in acommunication network 10. In some embodiments, a processor 32 mayconduct a handoff from a first communication route which has fallenbeneath some threshold voice quality score to a second route having anacceptable voice quality score (e.g., above 70 out of 100 or 75 out of100, etc.).

In some embodiments, a handoff in a multimedia network 10 may beconducted before a voice quality score falls beneath a threshold level.For example, a network may store the total voice quality metrics of acommunication device based on the spatial location of the device. Suchinformation may be stored in any suitable storage unit (e.g., thenetwork information query unit 62 and/or the information computed by theRF link quality analysis unit 64) of the network 10, and a suitableprocessor (e.g., processor 32) may access the stored total voice qualitymetrics to predict when a handoff is likely necessary. For example, if auser typically moves from one location to another, which results in alow total voice quality metric and a necessary handoff, a preemptivehandoff may be made before the user moves to the location where voicequality becomes unacceptable. By conducting such preemptive handoffs,delays in establishing the handoff may be reduced. Thus, the user of amobile communication device may traverse a communication route whichresults in a necessary handoff. Furthermore, preemptive handoffs mayprovide a safety interval to allow consideration for other handoffroutes, should the usual handoff selection be impaired.

Furthermore, in some embodiments, a handoff may also be based on a costassociated with each possible communication route. For example, whileone communication route may have a higher voice quality score thananother, the processor 32 may still select a lower voice quality routebased on a cost comparison between the two routes. Furthermore,thresholds for acceptable voice quality score may be variable dependingon cost. Management of handoffs based partially on cost may becontrolled by a communication device user, or may be pre-programmed.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A method of managing a handoff in a multimedia communication network,the method comprising: computing a vocoder impairment based on thevocoder selected for a communication route in the network; computing aradio frequency (RF) link impairment based on one or more RF linksselected for the communication route; computing a subnetwork impairmentbased on the subnetwork selected for the communication route; computinga delay impairment based on a total delay incurred in transferring datathrough the selected vocoder, the selected one or more RF links, and theselected subnetwork; computing a total voice quality metric of thecommunication route based on the vocoder impairment, the RF linkimpairment, the subnetwork impairment, and the delay impairment; anddetermining whether and when to make a handoff based on the total voicequality metric of the communication route.
 2. The method of claim 1,wherein computing the vocoder impairment comprises determining abaseline quality level of the vocoder and an impairment factor of thevocoder due to either bit errors or packet losses.
 3. The method ofclaim 1, wherein computing the RF link impairment comprises estimatingdata loss incurred through the RF link and determining an impairmentfactor of the RF link due to bit errors or packet losses.
 4. The methodof claim 1, wherein computing the subnetwork impairment comprisesdetermining an impairment factor due to bit errors or packet losses foreach link in the subnetwork.
 5. The method of claim 1, wherein the delayimpairment is computed using one or more equations of the InternationalTelecommunication Union (ITU) E-model.
 6. The method of claim 1, whereindetermining whether and when to make a handoff comprises making ahandoff between a first communication route having a first total voicequality metric beneath a threshold level and a second communicationroute having a second total voice quality metric above the thresholdlevel.
 7. The method of claim 1, wherein determining whether and when tomake a handoff comprises making a handoff to a second communicationroute when a first communication route has a total voice quality metricwhich is lower than a second total voice quality metric of the secondcommunication route.
 8. The method of claim 1, wherein determiningwhether and when to make a handoff comprises making a handoff based on acost of a current communication route and costs of one or more othercommunication routes in the network.
 9. The method of claim 8, whereinmaking the handoff based on the cost is manageable by a user in thenetwork.
 10. The method of claim 1, comprising storing the computedtotal voice quality metric as a function of a spatial location of acommunication device in the network, and wherein determining whether andwhen to make the handoff comprises predicting a likely handoff based onthe stored total voice quality metric and conducting a preemptivehandoff based on the likely handoff prediction.